1. Field of the Invention
The present invention relates to a magnetic head, and in particular, to a magnetic head for use in a magnetic disc drive which executes magnetic recording/reproducing of information on/from a magnetic disc serving as a rotating recording medium.
2. Description of the Prior Art
Some conventional structures of such a magnetic head will be described with reference to FIG. 1A to FIG. 3B, for use in a floppy disc driver (to be called "FDD" for short hereinafter) executing recording/reproducing of information on/from a floppy disc, that is, a flexible rotating magnetic recording medium. FIG. 1A to FIG. 3B show respectively constructions of three kinds of magnetic heads different from each other. FIGS. 1A, 2A and 3A are front elevations, respectively showing medium-sliding surface side of magnetic heads, while FIGS. 1B, 2B and 3B are enlarged views of gap sections or parts of cores of the heads, respectively. Parts or sections common to or corresponding to all the figures are designated by the same or like reference numbers.
First, FIGS. 1A and 1B show a conventional example of a magnetic head of so-called tunnel erasing type for use in the in FDD for a disc whose recording capacity is 1-2 MB. In these figures, reference numeral 1 denotes a core assembly constructed as a combination in which a magnetic core 2 (called "a recording/reproducing core" hereinafter) for recording/reproducing, and an erasing magnetic core 4 (called "an erasing core" hereinafter) for erasing both ends of a recording track, that is, for executing so-called tunnel erasing are joined to each other.
The recording/reproducing core 2 has a magnetic gap 3 (called "a recording/reproducing gap" hereinafter) for recording/reproducing. The recording/reproducing gap 3 has a track width RW. Further, the erasing core 4 has a pair of erasing magnetic gaps 5 and 5' (called "erasing gaps" hereinafter) which have their respective track widths E and E'. Both ends of the recording/reproducing track width RW are erased with the erasing track widths E and E', so that information is recorded on the floppy disc in an effective track width RC between the erasing track width E and E'. In this connection, a sliding direction of a disc (not shown) with respect to the magnetic head is indicated by an arrow A shown in FIG. 1A.
A pair of non-magnetic sliders 7 and 8 are joined, by an adhesive or a glass material, respectively to both sides of the core assembly 1 composed of the recording/reproducing core 2 and the erasing core 4, to construct a magnetic head 10. The sliders 7 and 8 are, together with the core assembly 1, in sliding contact with the floppy disc (not shown) at a part of a sliding surface 9. Thus, the sliding contact of the core assembly 1 is stabilized, and the core assembly 1 is protected. Furthermore, each of the sliders 7 and 8 is made of a ceramic material.
Next, FIGS. 2A and 2B show an example of a conventional magnetic head of so-called precedence-erasing type, which is used in an FDD for a disc whose capacity is 4 MB. A difference of a magnetic head 10 from the conventional head shown in FIGS. 1A and 1B is, first, that arrangement of a recording/reproducing core 2 and an erasing core 4 is reversed. That is, the erasing core 4 is arranged upstream (on the side where the medium enters) of the recording/reproducing core 2 along a medium sliding direction indicated by the arrow A, to executed so-called precedence erasing. Moreover, an erasing gap 5 of the erasing core 4 is single and has an erasing track width EA. The erasing track width EA is identical with the sum of the erasing track widths E and E' and the effective track width RC of the example of the conventional type. In this connection, a track width RC of a recording/reproducing gap 3 of the recording/reproducing core 2 is also similar to one in the example of the conventional type shown in FIG. 1B. Further, the recording/reproducing core 2 and the erasing core 4 are joined to each other through a gap plate 6 which prevents magnetic interference between them.
In the magnetic head 10, since data are recorded by the recording/reproducing gap 3 after erasing has been executed by the erasing gap 5, there is no effect or influence of previous recording data when the first-mentioned data are rewritten or overwritten. Thus, it is also possible for a medium having large coercive force Hc to sufficiently overwrite the data.
Next, a magnetic head 10 illustrated in FIGS. 3A and 3B is used in-a further large-capacity type FDD. In the conventional magnetic head shown in FIG. 1A-FIG. 2B, the track density is 135 TPI (track pitch=0.1875 mm), whereas, in the magnetic head shown in FIGS. 3A and 3B, the track density is so improved as to be 405-1000 TPI. Then the track position control is executed by a servo signal with high accuracy. For this reason, as shown in FIG. 3B, the magnetic core becomes only a magnetic/reproducing core 2' having a recording/reproducing gap 3.
Furthermore, in this case, in order to improve the track density and also line recording density, the recording/reproducing gap 3 becomes a narrow gap. Accordingly, it is necessary to improve recording performance. For this reason, a thin film 11 of soft magnetic material with high permeability, made of an alloy of Fe-Al-Si series or the like, is made-up, so as to have a thickness of several .mu.m--several tens .mu.m, on confronting surfaces of the recording/reproducing core 2' made of ferrite, which are confronted with the thin film 11 through the recording/reproducing gap 3, by a thin-film forming technology such as sputtering, vacuum deposition or the like.
In connection with the above, a table in FIG. 4 illustrates various characteristics regarding the recording density of various FDDs for a 3.5 inch floppy disc, on which is mounted the conventional magnetic head described above. By the way, generally, in using FDDs, it is required to keep or maintain interchangeability between high ranking models and low ranking models which are different in recording capacity from each other, in order to retain interchangeability between software and data so as to provide a useful environment when used. For example, in the FDD for the 3.5 inch floppy disc illustrated in FIG. 4, some product whose capacity is 1.6 MB or 2 MB, is capable of writing and reading (hereinafter referred to as "R/W interchange") with respect to a disc of 1M capacity and another product whose capacity is 4 MB, is capable of R/W interchange of disc of 1 MB or 2 MB (1.6 MB) capacity. Since, however, these products which are 135 TPI in the track density of disc are the same, thus enabling R/W interchange. If the track densities are different from each other, the products are capable of reading data from a disc with low track density, but cannot execute writing data on it. That is, the products become a type such that interchange between the software and the data as conventionally performed cannot be carried out sufficiently. For example, since in recent years, capacity of processing software such as integrated software, image information, and data base or the like increases, there is a trend toward higher capacity of the FDD including usages such as backup of a hard disc or the like. Thus, there appear products having capacity on the order of 10 MB-50 MB including the product whose capacity is 12.5 MB or 16 MB as shown in FIG. 4. The track density of each of these FDDs is 405 TPI-1555 TPI which is three times or more than 135 TPI of the track density of the conventional FDDs. For this reason, in the conventional products, the low-ranking R/W interchange cannot be executed.
In view of the above, in order that the interchangeability can be maintained even if the track densities are different from each other, a magnetic head of a complex type has been proposed in which a magnetic core of the tunnel erasing type or the precedence erasing type and a magnetic core of a servo signal type are placed in parallel to each other in a track widthwise direction. An example of the conventional magnetic head is shown in FIG. 5. In this magnetic head 10, a core assembly 1 (for 135 TPI) similar to that shown in FIGS. 1A and 1B, and a recording/reproducing core 2' (for 405 TPI-1555 TPI) of the servo signal type similar to that shown in FIGS. 3A and 3B are placed in parallel to each other with a gap plate or partition 16 made of non-magnetic ferrite, ceramics, glass material or the like located therebetween. When the magnetic head of complex type constructed in this manner is used to execute recording/reproducing on or from a magnetic disc (not shown), the core assembly 1 and the recording/reproducing core 2' are used in suitable selection, depending upon a difference in the track density, whereby the R/W interchange between the high ranking models (10 MB-50 MB) and the low ranking models (1 MB-4 MB) is made possible.
In this magnetic head of complex type, however, there arises a problem of interference due to magnetic flux leakage between the core assembly 1 and the recording/reproducing core 2', that is, a problem of so-called crosstalk. For example, when reproducing is executed by a recording/reproducing gap 3 in the recording/reproducing core 2' of the high-ranking track density, another adjacent recording/reproducing gap 3 in the core assembly 1 of the low-ranking track density executes reproducing on a plurality of high-ranking tracks. For this reason, the magnetic flux flowing through the core assembly 1 becomes magnetic flux leakage so that the magnetic flux leakage flows into the high-ranking recording/reproducing core 2'. By such crosstalk, there arises great problems on formation of an FDD, such as a lack in reliability of data, and the like.
Further, since the core assembly 1 and the recording/reproducing core 2' are arranged adjacent to each other, spaces for a coil bobbin, a back core and the like (not shown) are limited, thus causing difficulty in designing the magnetic head, and an increase in the number of parts. This leads to an increase in the cost for parts, and an increased number of assembly processes, thus resulting in a significant rise in cost for manufacturing the magnetic head.
Furthermore, it is difficult for each of the gaps 3, 5 and 5' in the core assembly 1 as well as the recording/reproducing core 2', which are placed in parallel to each other in the sliding surface 9 with a predetermined distance, to be both in sliding contact with the floppy disc in a stable condition. Thus, there arise problems associated with characteristics such as deterioration in modulation, reduction in reproducing output, or the like.